The present invention relates generally to battery charging systems and, more particularly, to a charger and charge control system for charging batteries, such as lithium-ion batteries.
Efficiency and power advantages inherent to lithium-ion batteries have promoted the development and use of such cells in a variety of applications, such as laptop computers. Yet, such progress has prompted greater demand for lithium-ion configurations that consume still less power and space. Consequently, efficiency considerations remain important to systems and industrial applications that utilize battery technologies.
Charge must be supplied to batteries in order for them to, in turn, power their respective loads. A percentage of the charge supplied to a conventional battery system is lost during the charging process. In some instances, heat dissipation accounts for such loss. That is, as current flows through a system, it interacts with resistive characteristics of system components and wiring and produces a voltage, some of which is released as heat. Consequently, it may be necessary to increase the amount of charge supplied to a conventional battery system in order to compensate for power losses. However, the required increased charge can translate into still greater heat generation and power inefficiency, thereby requiring sufficient heat dissipation components to prevent damage to the charging system and the batteries.
Such inefficiency can further impact size requirements of lithium-ion configurations. Namely, heat dissipation attributable to power propagation losses often in mandates that designers distance hardware components to avoid overheating. Elevated temperatures within a system compounds heat management by increasing the resistive properties of wiring and components comprising the circuitry of conventional systems. Thus, the conductive properties of circuitry is further lowered and still more heat is generated.
Absent steps to protect battery cells and other components from excessive heat, such as fans, heat sinks or physical spacing, system performance will suffer and hardware damage may result. Such provision includes circuit designers positioning either or both a charger and charge control circuit away from each other and outside of the pack containing the batteries. In this manner, heat stresses attributable to the charging and control functions are mitigated by their respective lack of proximity.
While this physical distance may lessen exposure of the circuitry to heat complications, the spacing requirement may result in complexities of its own. For example, the physical separation requirement often causes a lithium-ion configuration to be bulky and cumbersome. Accommodating such systems can inflate costs and complicate routine maintenance, such as battery replacement. Associated size requirements can further impede storage and render the circuitry vulnerable to jarring. Required spacing of components may additionally mandate increased costs associated with the design and manufacture of the system. Namely, such spacing can complicate circuit layouts and require additional circuitry needed to realize hardware separation.
Consequently, there is need for an improved charging system for charging lithium-ion battery systems.
The present invention overcomes the foregoing and other shortcomings and drawbacks of battery charger and charge control system and methods heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
More particularly, the battery system achieves greater efficiencies and cell protection through the application of switchable transistors and monitoring methods. Charge control circuitry of the battery system measures voltage across each lithium-ion cell in order to sense a ceiling or basement threshold voltage. The circuitry may enable or disable one or more switchable transistors in response to detecting such a voltage extreme in a respective cell. Such action allows voltage to equalize as between the cells prior to resuming charging operations.
Similarly, the circuitry may monitor extreme temperatures proximate the cells and disconnect the cells from the charging circuitry in response to detecting an elevated temperature. As such, heat will dissipate and lower the temperature proximate the cells to a safe level before charging the lithium-ion cells resumes. The present invention further accounts for potentially low voltage scenarios in the lithium-ion cells by disconnecting them from a discharge device when a basement voltage extreme is detected. Such provision allows the charging circuitry time to raise the voltage of a critically low cell to a stable level. As with the above scenarios, the battery charger and charge control system resumes operations in response to sensing that the critical condition has been alleviated.
The above switching and heat efficiencies associated with the charger and charger control circuitry further allow them to mount within a common battery housing, facilitating more compact and robust implementation. To this end, the circuitry is preferably wired onto a common circuit board. As such, the charge and charger control circuitry work in concert to supply charge to the lithium-ion batteries. The configuration of the charger and charger control circuitry additionally accommodates simultaneous charging of the cells as they provide a load to a discharge device.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.